# CVE-2026-44727: jupyter-server: Jupyter Server is the backend for Jupyter web applications

CVE-2026-44727 is fixed in 4 products on 1 platform, first by FEDORA-2026-275D2ECBBD, released June 26, 2026. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2026-44727
- Priority: Routine
- CVSS: 5.4 (medium)
- EPSS: 0.0044
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Jun 22, 2026

## Description

Jupyter Server is the backend for Jupyter web applications. Prior to 2.20, the nbconvert HTTP handlers in jupyter_server render user-authored notebook HTML under the Jupyter origin without a sandbox directive in their Content-Security-Policy. Combined with nbconvert.HTMLExporter's default non-sanitizing behavior, a notebook carrying an HTML payload in a display_data output triggers stored XSS with cookie access, full /api/* authority, and kernel RCE. This vulnerability is fixed in 2.20.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | jupyter-server Debian 14 | 2.20.0-1 | [DEBIAN-CVE-2026-44727](https://patchblox.com/security/data/fix/linux/debian-cve-2026-44727.md) | Jul 18, 2026 |
| Linux | python-jupyter-server Fedora 43 | 2.20.0-1.fc43 | [FEDORA-2026-275D2ECBBD](https://patchblox.com/security/data/fix/linux/fedora-2026-275d2ecbbd.md) | Jun 26, 2026 |
| Linux | python3-jupyter-server Fedora 43 | 2.20.0-1.fc43 | [FEDORA-2026-275D2ECBBD](https://patchblox.com/security/data/fix/linux/fedora-2026-275d2ecbbd.md) | Jun 26, 2026 |
| Linux | python3-jupyter-server+test Fedora 43 | 2.20.0-1.fc43 | [FEDORA-2026-275D2ECBBD](https://patchblox.com/security/data/fix/linux/fedora-2026-275d2ecbbd.md) | Jun 26, 2026 |

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Data as of 2026-11-08T13:06:02Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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